1. Field of Invention
The present invention refers to a membrane unit adapted for use in a housing of a pressure measuring unit which unit is preferably adapted to measure the pressure in an extra-corporeal blood circuit. Such pressure measuring units are usually referred to as “dome” or “pressure dome”. These units comprise a membrane forming one surface of a pressure measuring chamber which membrane in use is in contact with a fluid and with a pressure transducer for converting pressures and pressure changes of the fluid into electrical signals.
2. Description of the Prior Art
A pressure measuring unit comprising a membrane and a housing is known from U.S. Pat. No. 5,614,677. The pressure measuring unit disclosed in this document comprises a housing comprising a pressure measuring chamber which is in fluid communication with an inlet and outlet of the housing. One surface of the pressure measuring chamber is formed by a membrane which is fixed to the housing by means of a tension ring inserted in a groove on the upper surface of the housing. The tension ring is fixed in its position by aid of a guide of the transducer which is abutting the upper surface of the housing.
Prior art document WO99/37983 also discloses a pressure measuring unit comprising a housing with a pressure measuring chamber one surface of which is formed by a membrane. The membrane comprises a circumferentially extending bead which is located on the side of the membrane facing the measuring chamber and which is pressed into a groove of the housing. A similar arrangement is known from U.S. patent application US 2004/0050168 A1.
The pressure measuring units described in the prior art are disadvantageous as the mounting of the membrane to the housing is cumbersome or has to be established by the membrane itself which is made of soft material.